With the smart grid becoming the focus of current study， distributed generations（DGs） as one of the main functions in smart grid are increasingly widely applied in power systems，and the optimal allocation of DGs has become particularly crucial. A review is made of the optimal allocation of DG， with its current development at home and abroad summed up and analyzed. Some common optimization allocation models are given， especially those of comprehensive multi-objective optimization based on single-objective optimization. Optimization allocation methods are boiled down to analytic methods， heuristic methods， and probability optimization methods plus those for multi-objective optimization. Finally， optimization allocation of DGs in the micro-grid is discussed， with the future development of DG and micro-grid optimization projected.